1. Field of the Invention
The present invention relates generally to the field of injection stretch blow molding machines and, more particularly, to a mechanism for accurately adjusting the position of the blow mold sections on such a machine.
2. Discussion of the Prior Art
Conventional stretch blow molding machines have an elongated blow core that is inserted a short distance into the open mouth of a preform at the blow station for the purpose of then injecting a surge of high pressure air into the warmed and softened body of the preform to stretch it quickly into the recesses of a mold cavity defined by blow mold sections encapsulating the preform. A stretch rod normally associated with the core also moves through a quick stretching stroke to mechanically engage and stretch the body of the preform in cooperation with the air charge during the blow cycle. The blow core and stretch rod are then withdrawn, the mold sections are retracted, and the finished product is removed from the blow station.
A pair of thread splits support the preform and position it at the blow station as the pair of blow mold sections are brought together around the preform and engage the splits. A push-up plate assembly underlies the station, and is moved upward as the mold sections are brought together, defining a bottom end of the mold cavity. Typically, the mold sections are supported on separate platens that are moved toward and away from one another to enclose the preform prior to a stretch blow molding operation, and to release the finished molded product.
Each mold section is supported on a platen by a back plate to which the mold is secured. The back plate, in turn, is secured to the platen by threaded fasteners or the like. Accurate measurements must be made at the time the back plates are secured to the platens to insure that the mold elements are aligned with the thread splits. If the mold sections are out of alignment even slightly, numerous problems may arise.
For example, such misalignment can cause too much load to be exerted on the splits by the mold sections, causing the splits to stick to the mold sections as the sections are separated from one another upon completion of a molding operation. When the splits come free of the mold sections, they snap back against the molded product, frequently damaging it. Further, variations between the stack dimensions of different stretch blow molding machines can result in misalignment between the thread splits of the machines and the mold sections.
When mold sections are misaligned relative to the thread splits, through wear, improper set-up, or any other reason, it is necessary to remove the back plates from the platens, and to modify the plates before resecuring them to the platens. For example, in order to raise the mold elements, shims may be positioned beneath side rails of the back plates. Alternately, to lower the sections, wear pads provided on the back plates may be ground. Other ways of conventionally adjusting the position of the mold sections include machining the top of the mold or adjusting the position of the sections on the back plates.
Because of the size of many molds, some of which include mold sections for forming several bottles at a time, it is frequently necessary to employ a crane for moving the back plates and mold sections between the platens and a work bench at which such machining or refitting may be done. Thus, such adjustments are expensive, time consuming, and place the mold sections, many of which are highly polished, at risk of being damaged.